Thursday, September 8, 2011

ScienceDaily (Sep. 8, 2011) — Water softening
techniques are very effective for removing minerals such as calcium and
magnesium, which occur as positively-charged ions in "hard" water. But
many heavy metals and other inorganic pollutants form negatively-charged
ions in water, and existing water treatment processes to remove them
are inefficient and expensive.

Chemists at the University of California, Santa Cruz, have now
developed a new type of material that can soak up negatively-charged
pollutants from water. The new material, which they call SLUG-26, could
be used to treat polluted water through an ion exchange process similar
to water softening. In a water softener, sodium ions weakly attached to a
negatively-charged resin are exchanged for the hard-water minerals,
which are held more tightly by the resin. SLUG-26 provides a
positively-charged substrate that can exchange a nontoxic negative ion
for the negatively-charged pollutants.
"Our goal for the past 12 years has been to make materials that can
trap pollutants, and we finally got what we wanted. The data show that
the exchange process works," said Scott Oliver, associate professor of
chemistry at UC Santa Cruz.
The chemical name for SLUG-26 is copper hydroxide ethanedisulfonate.
It has a layered structure of positively-charged two-dimensional sheets
with a high capacity for holding onto negative ions. Oliver and UCSC
graduate student Honghan Fei described the compound in a paper that will
be published in the journal Angewandte Chemie and is currently available online.
The researchers are currently focusing on the use of SLUG-26 to trap
the radioactive metal technetium, which is a major concern for long-term
disposal of radioactive waste. Technetium is produced in nuclear
reactors and has a long half-life of 212,000 years. It forms the
negative ion pertechnetate in water and can leach out of solid waste,
making groundwater contamination a serious concern.
"It's a problem because of its environmental mobility, so they need new ways to trap it," Oliver said.
In their initial studies, the researchers used manganese, which forms
the negative ion permanganate, as a non-radioactive analog for
technetium and pertechnetate. The next step will be to work with
technetium and see if SLUG-26 performs as effectively as it did in the
initial studies.
"Whether or not it can be used in the real world is still to be seen, but so far it looks very promising," Oliver said.
This research was supported by the National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Santa Cruz. The original article was written by Tim Stephens.